Photoelectric relay



Jan. 11, 19384 N; SHRADER 2,104,825

PHOTOELECTRIC RELAY Filed Sept. 28, 1934 Iii/ 9. i

INVENTOR v TERRY M. SHRADER w iu/f ATTO R N EY Patented Jan. 11, 1938 PATENT OFFICE PHOTOELICTBIC RELAY Terry M. Shrader, West Summit, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application September 28, 1934, Serial No. 745,905

comm.

My invention relates to electrical relays and similar devices, more particularly to circuit opening and closing relays which will respond to very small currents.

Electromagnetic relays for opening and closing circuits may be made sufllciently sensitive to operate on small currents, but the expense of such relays increases, and their ruggedness decreases so rapidly with increase in sensitivity that such relays designed for high sensitivity and to operate at very small currents, for example less than a few microamperes, have not been commercially practical on account of the high cost and lack of ruggedness. A photoelectric tube is frequently used in conjunction with an electric relay to furnish a light operated electric switch operating on very small currents. However, a thermionic amplifier is usually necessary between the phototube and relay because the phototube current is too small for direct operation of the rugged relay 0! conventional design, generally used because of practical objections to the high sensitivity relay. In an arrangement making use of a phototube, amplifier and electromagnetic relay the time lag is sometimes appreciable and it is usually necessary to use relatively high voltages in connection with the amplifier. I

One object of my invention is to provide a commercially practical relay which will control a work circuit and will respond to small currents, for example, less than a few microamperes, and may be operated by means of a photoelectric responsive device.

Another object of my invention is to provide a relay which may conveniently be mounted in a vacuum tube containing an electronic device for operating the relay and thus obtain a simple, compact and rugged device having the advantages of a vacuum make and break relay.

A further object of my invention is to provide a simple and compact photo-relay which will open and close a work circuit in response to variations in light intensities and which is a unitary device which may be utilized to replace the usual phototube, amplifier and electromagnetic relay.

A still further object of my invention is to provide a photo-relay which has a trigger-like action, is free from appreciable time lag, and which will operate at low voltages.

In accordance with the preferred embodiment of my invention a pair of relatively movable contacts connected in the circuit to be controlled, are mounted in a sealed evacuated envelope which contains a rarefied atmosphere of gas or other ionizable medium capable of supporting a self-sustaining discharge between cold electrodes within the envelope. These contacts are moved by an actuator within the envelope and comprising, for example, a spring biased to close the contacts and a pair of cold electrodes, one of which expands and elongates when heated and which is connected to normally hold the spring against its bias so as to prevent closing of the contacts. The spacing of the cold electrodes and the pressure of the gas are so related that the normal operating voltage between the cold electrodes in insufiicient to start a discharge between them but will maintain a discharge once it is started. A photo-cathode in the envelope is so connected and positioned with respect to the cold electrodes that in response to a predetermined light intensity enough electrons leave the photo-cathode and enter the space between the two cold electrodes to ionize the gas and start a gas discharge between these two cold electrodes. This discharge is suflicient to heat and thereby elongate the electrode which is connected to the spring, thus permitting the spring to close the contacts. The relay will re-set itself to the open position if the voltage applied to the cold electrodes is alternating and the light source is removed since the gas discharge stops at each half cycle and will not be restarted in the absence of photo-cathode current.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a longitudinal section of a photo-relay showing the operating parts in perspective and constructed in accordance with my invention; Figure 2 is a partial vertical section of a modi flcation of the invention shown in Figure 1; Figure 31s a diagrammatic representation of the photo-relay and a circuit suitable for use with the photo-relays shown in Figures 1 and 2.

As shown in Figure l, the photo-relay is provided with an envelope l0 having the usual base H at one end and contact caps i2 and. I3 at the other, and encloses the electrodes which are mounted on the usual press H. The envelope contains an ionizable medium, for example, argon, neon, helium or like gas for supporting a self-sustaining discharge thru the envelope.

The circuit opening and closing device, which is mounted in the top of and fused to the envelope, comprises a dome shaped receptacle Ii, preferably of insulating material such as glass, closed at its lower end by means of a fiexible diaphragm I6, which extends transversely of the envelope. The envelope is thus divided into two separate chambers. A stationary contact I! is mounted within the receptacle by means of the lead-in conductor I8 connected to cap I3, and cooperates with the movable contact I 9, supported on the fiexible diaphragm I6. The flexible metal diaphragm I6 and contact I9 are connected by the lead 20 to the cap I2. The receptacle I5 is exhausted prior to being inserted within the envelope so that the pressure within the receptacle is substantially the same as that within the envelope I 0, after the envelope I0 has been sealed off. Due to the fact that the receptacle I5 is substantially free of air, the contacts will stand up for a long time because of the absence of oxidation and pitting due to sparking. While the receptacle is provided primarily to prevent ionization between the contacts thru the gas when a voltage is applied to the contacts, under some conditions the contacts may be mounted directly within the envelope without the receptacle, without having ionization occur.

Operation of the contacts is accomplished by means of the flexible spring 25 connected to diaphragm I6 and contact I9 by means of the insulating connector 26 and biased to move the flexible diaphragm upwardly to close the contacts. This spring is supported on the supported rod 21 embedded in the press II.

A cold electrode 28, preferably a filament of tungsten or molybdenum, is secured at one end by means of a connecting insulating bead 29 to the spring 25 and at the other to a lead 30 embedded in the press. The cold filamentary electrode normally holds the spring 25 down to prevent closing of the contacts III9. The other cold electrode, between which and the cold filamentary electrode a voltage just below the voltage necessary to start the discharge is applied, is preferably in the formof a grid 3i. The photo-cathode 32 is positioned to project electrons into the space between the two cold electrodes when exposed to a predetermined intensity of light whereby sufiicient ionization will occur between the two electrodes to start the discharge between them, causing the cold filament electrode to be heated and to expand thus permitting the spring 25 to move up and close the contacts.

The operation of the photo-relay may be explained by referring to Figure 3. There is normally provided between the cold grid-like electrode 3I and cold filament electrode 23 an A--C voltage, for example, 110 volts, and having connected across the same a resistor 33. The pressure of the gas and the spacing of the cold electrodes 28 and 3| is such that at normal operating voltage a gas discharge is just on the verge of starting between the cold electrodes, that is the operating voltage is just below the breakdown voltage. Under these conditions the contacts are maintained in the open position. When sufficient light falls upon the photo-cathode 32, which is connected to the mid-point of the resistor 33, the emission from the photo-cathode introduces photo-electrons, into the space between the grid and filament electrodes, thereby starting the gas discharge between these electrodes whereupon the temperature of the filament electrode increases perceptibly causing it to immediately expand, thus elongating and permitting the spring 25 to close the contacts II-I3. Thus, with every portion of a cycle during which the cold filament electrode is positive the discharge fiows from the cold grid 3| to the filament electrode 28, thus maintaining the filament at a sumciently high temperature so that the contacts remain closed so long as the light intensity exceeds a predetermined value. Due to the fact that the gas discharge is interrupted each half cycle, the photo-relay becomes selfsetting inasmuch as when an insufficient number of photo-electrons are supplied to the grid filament space ionization will not take place, and substantially no heat is developed in the filament electrode to expand the filament electrode to increase its length.

A modification of the means shown in Figure 1 for preventing a discharge between the contacts controlling the work circuit is shown in Figure 2, where the contact 35 is provided with the circular shield 36 and is mounted in the top of the envelope by means of the lead 31 connected to a top cap 33. The lower movable contact 38 provided with a shield 40 is supported on the actuating spring 4| connected by the lead 42 to the cap 43, the spring 4| being insulated from support 21 by insulating member 44. The space between the contacts and shield is less than the mean free path of the electrons with the gas pressure in the tube. It is, of course, understood that the gas pressures may be used such that no means will be necessary to prevent a gas discharge between the contacts under the voltage conditions prescribed. The shields extend very close to the walls of the envelope to prevent a gas discharge around their edges. It is of course understood that the form of cold electrode which closes the contacts may take different forms; for example, it may consist of a bi-metallic strip which bends in response to thermal conditions to close the contacts.

It will thus be seen that I have provided a very simple and rugged photo-electric relay which eliminates the necessity for amplifiers and electro-magnetic relays and which is not only sensitive to small changes of light intensity but also eliminates the necessity for high voltages for the amplifier and is capable of controlling circuits in which the current is of a value of several amperes with no appreciable time lag in the operating device. The contacts are capable of handling up to about 5 amperes at 110 volts.

While I have indicated the preferred embodimerits of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is- 1. A photo-relay including an envelope containing an ionizable medium, and enclosing a pair of spaced cold electrodes between which a voltage may be applied just below that at which breakdown will occur between said electrodes, a photo-cathode within said envelope adjacent said electrodes to start ionization of said ionizable medium between said pair of electrodes when said photo-cathode is exposed to a predetermined light intensity, one of said pair of electrodes comprising a material which expands in response to temperature changes when ionization takes place, and a circuit opening and closing device connected with said one of said pair of electrodes to be controlled thereby.

2. A photo-relay including an envelope containing an ionizable medium and enclosing a cold filament electrode and cold grid electrode surrounding said filament electrode and between which cold electrodes a voltage may be applied just below the voltage which will start a discharge between said electrodes, a photo-cathode positioned adjacent to said cold electrodes to start ionization of said ionizable medium between said electrodes when said photo-cathode is exposed to predetermined light intensity, said filament electrode comprising a material which expands in response to increase in temperature when ionization occurs, and a pair of circuit opening and closing contacts one of said contacts being connected to said filament electrode and controlled by said filament electrode.

3. A photo-relay including an envelope containing an ionizable medium and enclosing a cold filament electrode, and a cold grid electrode surrounding said cold filament electrode and between which electrodes a voltage may be applied just below the voltage which will start a discharge between said cold electrodes, 8. photocathode positioned adjacent said cold electrodes to start ionization of said ionizable medium between said cold electrodes when said photo-cathode is exposed to a predetermined light intensity, said filament electrode comprising a material which expands in response to increase in temperature when ionization occurs, a pair of circuit opening and closing contacts within said envelope, a spring connected to one of said contacts and biased to close said contacts, said filament electrode being connected to said spring and contacts to normally maintain said contacts in open position against the bias of said spring when said filament is cold.

4. A photo-relay including an envelope containing an ionizable medium and enclosing a cold filament electrode, and a cold grid electrode surrounding said filament electrode and between which electrodes a voltage may be applied just below the voltage at which a discharge will take place between said cold electrodes, a photo-cathin temperature when ionization occurs, pair of circuit opening and closing contacts biased to close, said filament electrode being connected to one of said contacts to normally maintain said contacts in open position when said filament is cold and means adjacent said contacts to prevent a gas discharge therebetween.

5. A photo-relay including an envelope containing an ionizable medium and enclosing a cold filament electrode, and a cold grid electrode surrounding said filament electrode and between which electrodes a voltage may be applied just below the voltage at which breakdown will occur between said electrodes, a photo-cathode adjacent to said cold electrodes positioned to start ionization of said lonizable medium between said electrodes when said photo-cathode is exposed to predetermined light intensity, said filament electrode comprising a material which expands in response to increase in temperature when ionization occurs, a stationary contact mounted in one end of said envelope, a flexible diaphragm mounted adjacent said contact and extending transversely of the envelope, a movable contact mounted on said flexible diaphragm to cooperate with said stationary contact, and means biased to move said diaphragm to close said contacts, said cold filament electrode being connected to the biased means for normally maintaining said contacts in an open position when there is no ionization.

6. A photo-relay including an envelope containing an ionizable medium and enclosing a cold filament electrode and a cold grid electrode surrounding said filament electrode and between which electrodes a voltage may be applied just below the voltage which will start a discharge between said electrodes, a photo-cathode positioned adjacent said cold electrodes to start ionization between said electrodes when said photocathode is exposed to a predetermined light in tensity, said filament electrode comprising a ma" terial which expands in response to increase in temperature when ionization occurs, a pair of relatively movable contacts biased to close and provided with metallic discs extending transversely of the envelope and spaced less than the distance of the mean free path of an electron in the ionizable medium, said filament electrode being connected to one of said contacts for controlling operation of said contacts.

TERRY M. SHRADER. 

